The present invention relates to a class of silicone-containing monomers and their use in contact lens materials, especially silicone-containing contact lens materials. The monomers are especially useful in reducing modulus of silicone-containing contact lens materials.
Hydrogels represent a desirable class of materials for many biomedical applications including contact lenses. Hydrogels are hydrated, cross-linked polymeric system that contain water in an equilibrium state. Silicone hydrogels are a well known class of hydrogels and are characterized by the inclusion of a silicone-containing material. Silicone-containing monomers may be copolymerized with a wide variety of hydrophilic monomers to produce a variety of silicone hydrogel products. Either the silicone-containing monomer or the hydrophilic monomer may function as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable functionalities) or a separate crosslinker may be employed.
Many silicone hydrogels possess relatively high modulus (Young's modulus of elasticity). For many biomedical applications, including contact lens applications, it is desirable to provide hydrogels having reduced modulus, e.g. in the range of about 20 g/mm.sup.2 to about 150 g/mm.sup.2, and more preferably from about 30 g/mm.sup.2 to about 100 g/mm.sup.2. This is particularly important in the formation of soft contact lenses, as the modulus of the lens material can have a significant impact upon lens "comfort." Lenses possessing high modulus often have a perceived stiffness which may result in an unnatural feeling when worn upon the eye.
Another class of silicone materials useful for contact lens applications are non-hydrogels (referred to herein as "low water" materials). Low water silicone materials, like their hydrogel counterparts, are a copolymer of a silicone-containing monomer, however, unlike silicone hydrogels, "low water" silicone materials do not include appreciable amounts of hydrophilic monomers and/or internal wetting agents (i.e. typically less than 5 weight percent). As such, low water silicone materials, as their name suggest, do not absorb or retain appreciable amounts of water, e.g. less than about 5 weight percent, and more typically less than about 1 or 2 weight percent.
Although low water silicone compositions have very desirable oxygen permeability, they typically possess relatively high modulus (Young's modulus of elasticity). As for hydrogel contact lenses, the modulus of the lens material can have a significant impact upon lens "comfort."
U.S. Pat. Nos. 5,710,302 and 5,714,557 describe a class of silicone-containing monomers that are useful for reducing the modulus of silicone hydrogel or low water polymeric silicone compositions. The present invention provides additional silicone-containing monomers useful for reducing the modulus of such materials.